JPH11211982A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the zoom lens with short overall length which has high optical performance over the entire power variation range and a power variation ratio of nearly 2, and consists of two lens group. SOLUTION: This zoom lens has a 1st group with positive refracting power and a 2nd group with negative refracting power in order from the object side; and the 2nd group which varies the power by varying the gap between both the lens groups has a positive meniscus lens 21 which is convex to the image plane side and a negative meniscus lens 22 which is convex to the image plane side and the object-side lens surface of the lens 22 consists of an aspherical surface which decreases in negative refracting power from the lens center to the lens periphery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens having a short back focus comprising two lens groups suitable for a lens shutter camera, a video camera, and the like, and more particularly, to an aberration by appropriately setting a lens configuration of each lens group. The present invention relates to a zoom lens having a variable magnification ratio of about 2 which performs satisfactory correction and shortens the overall length of the lens (the distance from the first lens surface to the image surface).

[0002]

2. Description of the Related Art Recently, an aspherical lens has been effectively used as a zoom lens for a lens shutter camera, a video camera, and the like, and the number of lenses has been reduced and the overall length of the lens has been shortened and simplified. Various zoom lenses have been proposed.

As a simple zoom lens for a lens shutter camera that does not require a long back focus, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power are sequentially arranged from the object side. Many so-called two-unit zoom lenses having a relatively short overall lens length and having a variable magnification by changing the distance between both lens units have been proposed.

[0004] The present applicant has previously disclosed Japanese Patent Application Laid-Open No. 56-128911.
JP, JP-A-57-201213, JP-A-57-201213
JP-A-170816, JP-A-60-191216, JP-A-62-56917, and the like, in order from the object side, a first group having a positive refractive power and a second group having a negative refractive power.
A small so-called two-unit zoom lens, which includes one lens unit and changes the magnification by changing the distance between the two lens units, has been proposed.

In this publication, a two-unit zoom lens having high optical performance, which employs positive and negative refractive power arrangements in order from the object side, has a relatively short back focus and shortens the entire length of the lens. Have achieved.

[0006] For example, Japanese Patent Application Laid-Open No. Sho 56-128911
In the publication, the first group is composed of four lenses of positive, negative, positive and positive, and the second group is composed of two lenses of positive and negative, so as to simplify the entire lens system, and a compact zoom. Suggest a lens.

As another two-group zoom lens, Japanese Patent Laid-Open No.
In Japanese Patent Application Laid-Open No. 3-31224, the first unit includes four lenses of positive, negative, positive, and positive, and the second unit includes two positive and negative lenses, and each lens unit uses an aspheric surface. A small zoom lens with improved optical performance has been proposed.

In Japanese Patent Application Laid-Open No. 4-161914, the first unit is composed of four lenses: a positive lens, a negative lens, an aspherical lens and a positive lens, and the second unit is composed of three positive, negative and negative lenses.
There has been proposed a zoom lens composed of a plurality of lenses and using an aspheric surface for each lens group.

Further, JP-A-62-90611, JP-A-62-113120, and JP-A-3-116110
In the publication, the first unit is composed of four lenses of positive, negative, negative and positive, and the second group is composed of two lenses of positive and negative or three lenses of positive, negative and negative. A two-unit zoom lens with a ratio of about 1.5 has been proposed.

[0010]

SUMMARY OF THE INVENTION In the above-described two-unit zoom lens including the first lens unit having the positive refractive power and the second lens unit having the negative refractive power, the size of the entire lens system is reduced. In order to obtain a good optical performance over the entire zoom range, having a zoom ratio of about 2 times, appropriately set the lens configuration of each lens group and use an aspheric surface of an appropriate shape for each lens group. This is very effective in correcting aberrations.

On the other hand, Japanese Unexamined Patent Publication No. Sho 63-31122 discloses
4, Japanese Patent Application Laid-Open No. 62-90611,
The zoom lens proposed in Japanese Patent Publication No. 116110 tends to have a relatively long overall lens length.

In particular, in a compact camera or the like having a mechanical structure in which the distance from the first lens surface to the final lens surface at the telephoto end becomes longer and the lens is collapsed when the camera is carried, it can be said that the entire lens system is not necessarily small. Did not.

In the zoom lens proposed in Japanese Patent Application Laid-Open No. 4-161914, the aspherical lens is made of a plastic material to make it easy to manufacture. However, at the telephoto end, the distance from the first lens surface to the final lens surface is increased. However, it was not suitable as a compact camera that collapsed the lens barrel when carrying it.

According to the present invention, in a so-called two-unit zoom lens, by appropriately setting the lens configuration of each lens unit and effectively using an aspherical lens, the total lens length can be shortened at a zoom ratio of about 2. It is an object of the present invention to provide a compact zoom lens having high optical performance over the entire zoom range.

[0015]

The zoom lens according to the present invention is roughly classified into the first invention, the second invention, and the third invention.
Includes two inventions. Hereinafter, the first invention, the second invention, and the third invention are collectively referred to as the present invention.

First, the zoom lens according to the first invention is:
(1-1) A zoom lens having two lens groups, a first group having a positive refractive power and a second group having a negative refractive power, in order from the object side, and performing zooming by changing the distance between the two lens groups. The second group has two lenses, a meniscus-shaped positive twenty-first lens having a convex surface facing the image surface side and a meniscus-shaped negative twenty-second lens having a convex surface facing the image surface side. The lens surface on the object side of the lens is formed of an aspheric surface having a shape in which negative refractive power becomes weaker from the center of the lens toward the periphery of the lens. The refractive index and Abbe number of the material of the 22nd lens are Nd22 and νd2, respectively.
2. The focal length of the i-th lens unit is fi, the focal length of the entire system at the wide-angle end is fw, and the back focus at the wide-angle end is b.
fw, when the maximum image height of the effective screen is Y, 0.5 <f1 / fw <0.8 (1) -0.8 <f2 / fw <-0.5 (2) 1 .65 <Nd22 <1.85 (3) 40 <νd22 <60 (4) 0.2 <bfw / Y <0.5 (5) .

The zoom lens according to the second aspect of the present invention includes (1-
2) A zoom lens having two lens groups, a first group having a positive refractive power and a second group having a negative refractive power, in order from the object side, and performing zooming by changing the distance between both lens groups. 1st group is 1st
a group, an aperture, a first lens group having a positive refractive power, the first lens group has at least one aspheric surface, and the second lens group has a positive twenty-first lens and an object-side lens surface. Is an aspherical negative second lens, and the focal length of the i-th group is fi,
When the focal length of the entire system at the wide-angle end is fw and the focal length of the first lens group is f1b, 0.5 <f1 / fw <0.8 (1) -0.8 <f2 / fw <- 0.5 (2) 0 <fw / f1b <0.3 (6) The condition is satisfied.

The zoom lens according to the third aspect of the present invention includes (1-
3) A zoom lens that has two lens groups, a first group having a positive refractive power and a second group having a negative refractive power, in order from the object side, and performs zooming by changing the distance between both lens groups. 1st group is 1st
group a, and a first group b having a positive refractive power. The first group b includes a negative thirteenth lens including an aspherical surface having a shape in which the negative refractive power increases from the lens center to the lens periphery, and a positive fourteenth lens. The second group includes a positive twenty-first lens and a negative twenty-second lens having a non-spherical object-side lens surface. The focal length of the i-th group is fi, and the entire system at the wide-angle end is Is the focal length of fw and the focal length of the first lens group is f1b. 0.5 <f1 / fw <0.8 (1) -0.8 <f2 / fw <-0.5 (2) 0 <fw / f1b <0.3 (6) This condition must be satisfied.

[0019]

1 to 5 are sectional views of a lens at a wide angle end according to Numerical Examples 1 to 5 of the present invention.

In the figure, L1 denotes a first group having a positive refractive power, and L2 denotes a second group having a negative refractive power. The distance between the two lens groups is reduced and both lens groups are moved toward the object side as shown by arrows. Moving the zoom from the wide-angle end to the telephoto end.

The first lens unit L1 has two lens units, a first lens unit L1a and a first lens unit L1b having a positive refractive power. S
P denotes an aperture stop, which is disposed between the first lens unit L1a and the first lens unit L1b in the present invention, and moves integrally with the first lens unit with zooming. IP is an image plane.

The first unit L1 includes a positive meniscus eleventh lens having a convex surface facing the object side, a negative twelfth lens having a concave surface facing the object side, a diaphragm SP, and a concave lens surface on the object side. The fourteenth lens has a negative thirteenth lens whose concave surface is aspheric and a positive fourteenth lens whose both lens surfaces are convex. The aspheric surface of the thirteenth lens has a shape in which the negative refractive power increases from the center of the lens toward the periphery of the lens.

The second lens unit L2 includes a positive meniscus twenty-first lens having a convex surface facing the image surface side and a negative meniscus twenty-second lens having a concave lens surface on the object side and an aspheric concave surface. It has two lenses. Note that the aspheric surface of the 22nd lens has such a shape that the negative refractive power becomes weaker from the center of the lens toward the periphery of the lens.

In the zoom lens of the present invention, focusing is performed by extending only the first unit toward the object side, or extending the first and second units together while increasing the distance between both lens units. Has gone by.

In the present embodiment, such a zoom system and the lens configuration (1-1) or (1-2) as described above are used.
Alternatively, by adopting (1-3), it is possible to satisfactorily correct the aberration variation due to the zoom ratio of about 2 while reducing the overall length of the lens, particularly, the overall length of the lens at the wide-angle end. High optical performance over a double range.

Next, a description will be given of the features of the lens structure of the zoom lens composed of two groups according to the present invention.

In a so-called two-unit zoom lens comprising a first lens unit having a positive refractive power and a second lens unit having a negative refractive power, the refractive power of each lens unit is appropriately adjusted in order to reduce the size of the entire lens system. Otherwise, it is difficult to achieve both high optical performance and miniaturization.

In general, in a two-unit zoom lens, the first lens unit moves largely toward the object side at the telephoto end, so it is desired to reduce the total optical length at the telephoto end. On the other hand, it is also desired to reduce the lens diameter of the second group, which has a relatively large lens diameter.

Generally, if the refractive power of each lens unit is increased,
The total length of the optical system can be reduced, and at the same time, the lens diameter of the second group can be reduced. However, simply increasing the refractive power rapidly increases the amount of aberration generated in each lens group.
It is difficult to obtain high optical performance in the entire zoom range.

In particular, at the telephoto end, the second lens unit greatly enhances the imaging performance of the first lens unit. Therefore, it is difficult to obtain high optical performance while increasing the refractive power of the second lens unit. It becomes difficult to satisfactorily correct this.

Also, at the wide-angle end, coma, distortion,
Correction of curvature of field and the like also becomes difficult. Therefore, as a feature of the lens systems of the first to third inventions, the second group is constituted by a positive twenty-first lens and a negative twenty-second lens, and at least the negative second lens
On the object-side lens surfaces of the two lenses, an aspherical surface where the negative refractive power decreases from the lens center to the lens periphery is arranged.

In order to reduce the size of the entire lens system, the refractive power of the second lens unit must be increased. If the refractive power of the second lens unit is increased, distortion and coma aberration at the wide-angle end are deteriorated. At the telephoto end, the imaging performance of the first lens unit is enlarged by the second lens unit, so that it is difficult to correct spherical aberration. Becomes Therefore, by applying the above-mentioned aspherical surface, various aberrations generated by the strong negative refractive power of the second group are canceled out by making the negative refractive power weaker from the center of the lens to the periphery of the lens. Off-axis aberration and spherical aberration at the telephoto end are corrected in a well-balanced manner.

The first invention has the configuration (1-1), the second invention has the configuration (1-2), and the third invention has the configuration (1-3). Good optical performance is obtained.

In particular, the first to third inventions have a basic structure of a zoom lens composed of two groups, and two lens groups of a first group having a positive refractive power and a second group having a negative refractive power in order from the object side. And
Based on a configuration in which the magnification is changed by changing the distance between both lens groups, the first
In the invention, the second group includes two lenses: a positive meniscus twenty-first lens having a convex surface facing the image surface side, and a negative meniscus twenty-second lens having a convex surface facing the image surface side. Second
The lens surface on the object side of the two lenses is formed of an aspheric surface having a shape in which the negative refractive power becomes weaker from the center of the lens toward the periphery of the lens, and further satisfies the conditional expressions (1) to (5).

In the second invention, the first lens unit is a first lens unit,
An aperture having a first group of positive powers, the first group having at least one aspheric surface, and the second group having a positive second
One lens and a second negative lens in which the lens surface on the object side is aspherical
Conditional expressions (1), (2), (6)
To be satisfied.

In the third invention, the first lens unit has a first lens unit and a first lens unit having a positive refractive power. The negative refractive power of the first lens unit increases from the center of the lens to the periphery of the lens. The second group includes a negative thirteenth lens including a positive aspherical lens and a negative twenty-second lens having an aspherical object-side lens surface. , And further, conditional expressions (1), (2) and (6) are satisfied.

Next, the technical meaning of each of the above conditional expressions will be described.

Conditional expression (1) relates to the ratio between the focal length of the first lens unit and the focal length of the entire system at the wide-angle end, and is mainly for realizing the miniaturization of the lens system.

If the lower limit of conditional expression (1) is exceeded, the positive refractive power of the first lens unit becomes too strong, and it becomes difficult to correct the field curvature at the wide-angle end and the spherical aberration particularly at the telephoto end. Absent. On the other hand, when the value exceeds the upper limit, the positive refractive power of the first lens unit becomes too weak and the lens system becomes large, which is not good.

Further, in order to satisfy miniaturization and high optical performance, it is preferable to set the lower limit of conditional expression (1) to 0.55. It is desirable that the upper limit value be 0.75.

Conditional expression (2) relates to the ratio of the focal length of the second lens unit to the focal length of the entire system at the wide-angle end, and is mainly used to reduce distortion at the wide-angle end, field curvature, and downsizing of the lens system. belongs to.

If the negative refractive power of the second lens unit becomes too weak below the lower limit value of the conditional expression (2), especially in a two-unit zoom lens in which the total optical length increases at the telephoto end, a strong retrofocus type at the telephoto end. If not formed, it is not good because the overall length of the lens increases. If the negative refractive power of the second lens unit becomes too large beyond the upper limit, the light flux on the peripheral image plane passes through a position farther from the optical axis of the second lens unit, especially at the wide-angle end. It is difficult to correct the distortion generated in the zoom lens, and the distortion at the wide-angle end and the field curvature are deteriorated.

Further, in order to realize high optical performance and downsizing, it is preferable to set the lower limit of conditional expression (2) to -0.7. Further, it is desirable that the upper limit value be -0.55.

Conditional expression (3) defines the refractive index of the material of the 22nd lens having an aspheric surface in the second group, and is mainly used to satisfactorily correct image plane characteristics.

If the lower limit of conditional expression (3) is exceeded, the Petzval sum will increase too much in the negative direction, deteriorating the image surface characteristics. In addition, a lens shape capable of favorably correcting various aberrations especially at the wide-angle end. Is not good because it becomes difficult to set If the value exceeds the upper limit, the image surface characteristics can be corrected well, but in general, if the refractive index is high, the transmittance of the material is deteriorated, which is not good.

In order to maintain a balance between higher optical performance and cost, it is preferable to set the lower limit of conditional expression (3) to 1.70. Further, the upper limit is preferably set to 1.80.

The conditional expression (4) is for defining the Abbe number of the material of the 22nd lens having the aspheric surface of the second group.

If the variance exceeds the lower limit of conditional expression (4), the chromatic aberration of magnification and the axial chromatic aberration at the telephoto end become difficult to correct, which is not good. On the other hand, if the variance becomes too small beyond the lower limit, it becomes difficult to correct chromatic aberration of magnification especially at the wide-angle end, which is not good.

Further, in order to obtain high optical performance, it is desirable to set the lower limit of conditional expression (4) to 45. Further, it is desirable to set the upper limit to 55.

Conditional expression (5) relates to the ratio between the back focus (on-axis air gap from the last lens surface to the paraxial image plane) at the wide-angle end and the maximum image height, mainly for shortening the total lens length at the wide-angle end. belongs to.

If the lower limit value of conditional expression (5) is exceeded, the second unit will be too close to the image plane and the diameter of the lens of the second unit will increase, or the exit angle will be too tight and insufficient peripheral light will occur. It is not good because it becomes difficult to correct. On the other hand, when the value exceeds the upper limit, the total optical length at the wide-angle end increases, which is not preferable.

Conditional expression (6) appropriately sets the positive refractive power of the first lens subunit of the first lens unit, and satisfactorily corrects spherical aberration on the telephoto side together with the thirteenth lens having an aspheric surface. It is for. If conditional expression (6) is not satisfied, it becomes difficult to satisfactorily correct spherical aberration on the telephoto side.

In order to obtain higher optical performance in the first invention, it is preferable to satisfy at least one of the following conditions.

(A-1) When the focal lengths of the 21st lens and the 22nd lens are f21 and f22, respectively, the following condition is satisfied: -0.3 <f22 / f21 <-0.1 (7) It is to be.

The conditional expression (7) is a positive second
Regarding the ratio of the focal length between the first lens and the negative twenty-second lens,
It is mainly for favorably correcting various aberrations.

When the value exceeds the lower limit of conditional expression (7), the positive
If the refractive power of the lens becomes too strong, when the refractive power of the second group is set to a desired value, if the refractive power of the positive twenty-first lens is increased, the refractive power of the negative second lens will also be increased accordingly. Therefore, the negative influence of the negative refractive power in a balanced manner becomes stronger, and in particular, various aberrations at the wide-angle end tend to be difficult to correct, which is not preferable. If the refractive power of the positive twenty-first lens exceeds the upper limit and becomes too weak, the negative Petzval's sum increases, the image surface characteristic deteriorates, and the chromatic aberration is favorably corrected over the entire zoom range. This is not preferable because it tends to be difficult to take.

In order to obtain higher optical performance, it is preferable to set the lower limit of conditional expression (7) to -0.25. Further, it is desirable that the upper limit value be -0.15.

(A-2) When the radii of curvature of the lens surfaces on the object side and the image plane side of the 22nd lens are R23 and R24, respectively: -0.9 <(R23-R24) / (R23 + R24) <-0 .5 (8).

Conditional expression (8) is for appropriately setting the lens shape of the negative second lens in the second group.

If the lower limit of conditional expression (8) is exceeded, a negative second
The radius of curvature of the lens surface on the object side of the two lenses increases,
In particular, it is not preferable because it becomes difficult to correct astigmatism at the wide angle end. On the other hand, if the value exceeds the upper limit, the radius of curvature of the lens surface on the object side becomes too small, and it becomes difficult to correct distortion particularly at the wide angle end, which is not preferable.

In order to obtain higher optical performance, it is preferable to set the lower limit of conditional expression (8) to -0.88.
Further, it is desirable that the upper limit value be -0.65.

(A-3) The first lens unit includes a negative lens including an aspherical surface having a negative refractive power increasing from the lens center to the lens periphery.

In the first invention, it is preferable to provide an aspherical surface to the first lens unit in order to achieve higher optical performance and downsizing. In the first invention, an aspherical surface is used for the second lens unit.
In particular, it is effective at the wide-angle end, and is particularly effective at the telephoto end by using an aspherical surface for the first lens unit, so that further optical performance and further miniaturization can be achieved.

In the second and third aspects of the present invention, it is preferable to satisfy at least one of the following conditions in order to obtain higher optical performance.

(B-1) The focal lengths of the negative thirteenth lens and the positive fourteenth lens of the first subunit are set to f13 and f14, respectively.
-0.4 <f14 / f13 <-0.01 (9) This condition must be satisfied.

Conditional expression (9) is mainly for setting an appropriate lens arrangement with respect to the ratio of the focal length of the negative thirteenth lens to the positive fourteenth lens of the 1b group.

If the lower limit of conditional expression (9) is exceeded, the first positive
The refractive power of the negative thirteenth lens becomes stronger than that of the fourth lens, and the Petzval sum increases in the negative direction, which makes it difficult to correct the image plane in a balanced manner over the entire zoom range, which is not preferable. If the value exceeds the upper limit, the refractive power of the negative thirteenth lens becomes too weak, and the achromatizing effect is reduced, and it becomes difficult to suppress the fluctuation of the axial chromatic aberration during zooming.

In order to obtain higher optical performance, it is preferable to set the lower limit of conditional expression (9) to -0.25.
Further, it is desirable that the upper limit value be -0.03.

(B-2) When the refractive index and Abbe number of the material of the 22nd lens are Nd22 and vd22, respectively: 1.65 <Nd22 <1.85 (3) 40 <νd22 <60・ (4) The following condition must be satisfied.

(B-3) When the focal lengths of the twenty-first lens and the twenty-second lens are f21 and f22, respectively, the following condition is satisfied: -0.3 <f22 / f21 <-0.1 (7) It is to be.

(B-4) When the back focus at the wide-angle end is bfw and the maximum image height of the effective screen is Y, the following condition is satisfied: 0.2 <bfw / Y <0.5 (5) It is.

The structures (b-2), (b-3) and (b-
Each conditional expression (3), (4), (5), (7) in 4)
Has the same technical meaning as the conditional expression described above.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness in order from the object side,
Ni and νi are the refractive index and Abbe number of the glass of the i-th lens in order from the object side. Table 1 shows the relationship between the above-described conditional expressions and the numerical examples.

The aspherical surface has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis, a positive traveling direction of light, R is a paraxial radius of curvature,
When A, B, C, D, and E are aspherical coefficients, respectively

[0075]

(Equation 1) This is represented by “E−X” means “× 10 ^−X ”.

[0076]

[Outside 1]

[0077]

[Outside 2]

[0078]

[Outside 3]

[0079]

[Outside 4]

[0080]

[Outside 5]

[0081]

[Table 1]

[0082]

As described above, according to the present invention, in a so-called two-unit zoom lens, by appropriately setting the lens configuration of each lens unit and effectively using an aspherical lens, a zoom ratio of 2 is obtained. Thus, it is possible to achieve a compact zoom lens having high optical performance over the entire zoom range in which the overall length of the lens is reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 3 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 4 is a sectional view of a lens according to a numerical example 4 of the present invention.

FIG. 5 is a sectional view of a lens according to a numerical example 5 of the present invention.

FIG. 6 is an aberration diagram at a wide angle end according to Numerical Embodiment 1 of the present invention.

FIG. 7 is an intermediate aberration diagram of the numerical example 1 of the present invention.

FIG. 8 is an aberration diagram at a telephoto end in Numerical Example 1 of the present invention;

FIG. 9 is an aberration diagram at a wide angle end according to Numerical Example 2 of the present invention.

FIG. 10 is an intermediate aberration diagram of the numerical example 2 of the present invention.

FIG. 11 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention.

FIG. 12 is an aberration diagram at a wide angle end according to Numerical Example 3 of the present invention.

FIG. 13 is an intermediate aberration diagram of the numerical example 3 of the present invention.

FIG. 14 is an aberration diagram at a telephoto end in Numerical Example 3 of the present invention.

FIG. 15 is an aberration diagram at a wide angle end according to Numerical Example 4 of the present invention.

FIG. 16 is an intermediate aberration diagram of the numerical example 4 of the present invention.

FIG. 17 is an aberration diagram at a telephoto end in Numerical Example 4 of the present invention.

FIG. 18 is an aberration diagram at a wide angle end according to Numerical Example 5 of the present invention.

FIG. 19 is an intermediate aberration diagram of the numerical example 5 of the present invention.

FIG. 20 is an aberration diagram at a telephoto end in Numerical Example 5 of the present invention.

[Explanation of symbols]

 L1 First lens unit L2 Second lens unit L1a First lens unit L1b First lens unit SP Aperture IP Image plane d d line g g line ΔS Sagittal image plane ΔM Meridional image plane c Sine condition

Claims (10)

[Claims] 1. A zoom lens having a first lens unit having a positive refractive power and a second lens unit having a negative refractive power in order from the object side, and performing zooming by changing the distance between both lens units. The second group is a meniscus-shaped positive twenty-first lens having a convex surface facing the image surface side.
Meniscus negative second lens with the convex surface facing the lens and the image surface side
The lens surface on the object side of the twenty-second lens includes an aspheric surface having a shape in which negative refractive power becomes weaker from the center of the lens toward the periphery of the lens.
The refractive index and Abbe number of the material of the two lenses are Nd22 and ν, respectively.
d22, when the focal length of the i-th lens unit is fi, the focal length of the entire system at the wide-angle end is fw, the back focus at the wide-angle end is bfw, and the maximum image height of the effective screen is Y, 0.5 <f1 / fw < 0.8−0.8 <f2 / fw <−0.5 1.65 <Nd22 <1.8540 <νd22 <60 0.2 <bfw / Y <0.5 Zoom lens. 2. The lens system according to claim 1, wherein a condition of -0.3 <f22 / f21 <-0.1 is satisfied when the focal lengths of said 21st lens and 22nd lens are f21 and f22, respectively. Zoom lens. 3. When the radii of curvature of the object-side lens surface and the image-surface-side lens surface of the 22nd lens are R23 and R24, respectively, −0.9 <(R23−R24) / (R23 + R24) <
The zoom lens according to claim 1, wherein the following condition is satisfied. 4. The apparatus according to claim 1, wherein the first group includes a negative lens including an aspherical surface having a negative refractive power that increases from the lens center to the periphery of the lens.
2 or 3 zoom lenses. 5. A zoom lens having two lens groups, a first group having a positive refractive power and a second group having a negative refractive power, in order from the object side, and performing zooming by changing the distance between both lens groups. The first group has a first group, a diaphragm, and a first group of positive refractive power,
The first group has at least one aspherical surface, and the second group includes a positive twenty-first lens and a negative twenty-second lens whose lens surface on the object side is an aspherical surface. Is fi, the focal length of the entire system at the wide-angle end is fw, and the focal length of the first lens group is f1b. 0.5 <f1 / fw <0.8-0.8 <f2 / fw <- A zoom lens characterized by satisfying the following condition: 0.50 <fw / f1b <0.3. 6. A zoom lens having two lens groups, a first group having a positive refractive power and a second group having a negative refractive power, in order from the object side, and performing zooming by changing the distance between the two lens groups. The first group has a first group and a first group having a positive refractive power. The first group includes a negative aspheric surface having a shape in which the negative refractive power increases from the center of the lens to the periphery of the lens. The second group includes a thirteenth lens and a positive fourteenth lens, and the second group includes a positive twenty-first lens and a negative twenty-second lens whose lens surface on the object side is an aspheric surface. fi, when the focal length of the entire system at the wide-angle end is fw and the focal length of the first lens subunit is f1b, 0.5 <f1 / fw <0.8-0.8 <f2 / fw <-0.50 A zoom lens that satisfies the condition of <fw / f1b <0.3. 7. When the focal lengths of the negative thirteenth lens and the positive fourteenth lens of the first subunit are f13 and f14, respectively, the condition of -0.4 <f14 / f13 <-0.01 is satisfied. 7. The zoom lens according to claim 5, wherein: 8. The condition that the following condition is satisfied: 1.65 <Nd22 <1.8540 <νd22 <60, where the refractive index and Abbe number of the material of the 22nd lens are Nd22 and νd22, respectively. Item 8. The zoom lens according to item 5, 6, or 7. 9. The lens system according to claim 5, wherein a condition of −0.3 <f22 / f21 <−0.1 is satisfied when the focal lengths of said 21st lens and 22nd lens are f21 and f22, respectively. , 6, 7
Or 8 zoom lenses. 10. The back focus at the wide-angle end is represented by b
The zoom lens according to any one of claims 5 to 9, wherein a condition of 0.2 <bfw / Y <0.5 is satisfied, where fw is the maximum image height of the effective screen.